SIMULATING 3-DIMENSIONAL VORTEX MOTION BY A VORTEX BLOB METHOD

A three-dimensional vortex blob method was applied to calculate severa l vortex motions: the deformation of pseudo-elliptic vortex rings, the jet issuing from the pseudo-elliptic nozzle into flow of uniform velo city, the unsteady separated flow around a circular disk with an angle of attack, and the interaction of several vortex rings which approxim ately reproduced the Kolmogorov spectrum. In the first three cases, th e viscous diffusion of vorticity was included. The pseudo-elliptic vor tex rings experienced axis switching and split into a few deformed vor tex rings. Rolling-up vortices in the pseudo-elliptic jet had a symmet ric arrangement in the minor-axis plane and an antisymmetric arrangeme nt in the major-axis plane in the developing region; further downstrea m, the vortices were arranged antisymmetrically in both planes. The wa ke behind the disk normal to the main flow reproduced the spiral and c olumnar modes of instability. A problem in the three-dimensional vorte x method is that vorticity tends to diverge at a stage of evolution of the vortex motions. An approximate method of avoiding the divergence of vorticity is proposed.